Government regulations and consumer desires demand that vehicles continuously improve on fuel economy and emissions. At the same time, vehicle affordability is a concern, in light of the numerous automotive requirements and increasing costs. Accordingly, there is a need for more fuel efficient and low-emission engines that are also without added complexity and cost.
Electrically powered and hybrid (conventionally fossil fuel power in combination with electrical power) vehicles are a viable solution for reducing emissions and improving fuel economy. Such vehicles are becoming increasingly attractive alternatives to fossil fuel powered cars. Electric and hybrid vehicles require high voltage applications having relatively large capacity battery systems with relatively large amounts of power compared to a 12 V automobile storage batter. However, because of the high voltage requirements, significant safety concerns are raised.
Accordingly, high voltage battery management systems incorporate safety features and monitoring systems. For example, negative contactors of the high voltage battery packs are monitored to determine whether the negative contactor is open, closed, or in-between, in order to determine whether the high voltage battery pack can be safely connected and used within the vehicle.
Conventional high voltage battery management systems typically perform high voltage (HV) level control from the low voltage (LV) side of the board. That requires the HV sensors, actuators, and communication to be isolated from, and transported to, the LV side of the board by way of optical photomos or digital isolators. Such systems typically use a significant number, e.g., 14, isolation components between the high voltage side and the low voltage side of the board. Components of this type are expensive, and automotive qualified components of this type are limited.
Various methods have been used for contactor negative status detection. In one example, switching components, such as a photomos, may be used and controlled from the low voltage side of the board. The midpoint of the pack may be used as a main reference to all other voltage measurements and ground for active components. Voltages more negative than the midpoint, like the contactor negative, then require an operational amplifier as an active component, to invert the signal and allow the use of a positive voltage analog-to-digital converter (ADC). This results in an analog voltage measurement, from which, with detailed system knowledge, the resistance of the negative contactor can be determined. Due to interference with changing high voltage pack potential, however, as well as needed circuitry, this solution is expensive and may be inaccurate.
In another example, the voltage drop created by the load current through the negative contactor may be measured, resulting in a measurement of the contact resistance of the contactor. A load current is required, and at low load currents, a voltage drop is difficult to measure due to the low contact resistance of the contactor.
In yet another example, a voltage may be injected, and the effect of the DC link on the voltage may be measured to determine the contactor status. This method, however, may not be accurate, and more components may be needed to protect for higher voltage, as the voltage sourced used for injection is typically the HV Battery Pack itself.
Accordingly, a need exists for a simple solution to determine the negative contactor status, which is cost effective.